Avalanche Forecast

Issued: Mar 13th, 2018 4:59PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Persistent Slabs.

cgarritty, Avalanche Canada

Sea To Sky.

An overnight transition from rain to snow leaves us with some uncertainty for Wednesday. Expect the new snow to form touchy slabs in areas where it accumulates.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Tuesday night: Rain transitioning to wet flurries and bringing around 6 cm of new snow. Light south winds.Wednesday: Continuing flurries bringing about 5 cm of new snow. Light southwest winds. Freezing level to 1200 metres with alpine high temperatures of -4.Thursday: Mainly sunny. Light northeast winds. Freezing level to 1400 metres with alpine high temperatures around -5.Friday: A mix of sun and cloud. Light north winds. Freezing level to 1600 metres with alpine high temperatures around -3.

Avalanche Summary

Reports from Monday included observations of three natural size 2.5 loose wet avalanches that released from steep, rocky, south-facing slopes in the afternoon in the Whistler area.On Sunday there was a report of a skier triggered size 2 storm slab avalanche on a west aspect at 2400m. On Saturday there were several size 2.5 natural persistent slab avalanches reported. These were suspected to have run in the previous 24hours and were observed on northwest to east aspects between 1900 and 2000m. Additionally there have been several observations of skier triggered storm and wind slab avalanche size 1-2 mostly on northerly aspects between 1800 and 2000m.

Snowpack Summary

After a bout of light rain, light new snow amounts are expected to accumulate on the surface over Tuesday night and Wednesday. The new snow is accumulating above variable crust and moist snow that formed on the surface after days of warm temperatures and sunshine. The storm snow beneath this interface was previously redistributed by west and south winds.Last week's storms buried a weak layer composed of soft facets, surface hoar, and/or crust that is roughly 50-100 cm below the surface. This layer has produced whumpfing, sudden results in snowpack tests, and some remotely triggered avalanches. Lots of the activity has been on buried surface hoar on north aspects at upper treeline elevations. The snowpack is well settled and strong beneath this interface. Variable winds in the past month have built up cornices on many ridgelines. They will become touchier as temperatures rise and when they are subject to the strong late-winter sun on clear days.

Problems

Wind Slabs

Another light dose of new snow will promote the formation of thin new wind slabs in lee terrain on Wednesday. The new snow will bury older, larger wind slabs that may still be reactive to human triggering.

Don't just follow the crowd. Look for recent wind loading patterns and choose your line accordingly.Watch for wind-loaded pockets around ridgecrests and in the lee of exposed terrain features.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

A layer of surface hoar, sugary facets, and/or crust is buried 50-100 cm deep and has produced widespread whumpfing, concerning snowpack test results, and a few large remotely triggered avalanches. Upper treeline elevations are the greatest concern.

Cornice or wind slab releases may step down to deeper layers and result in large avalanches.Use increasingly conservative route selection while travelling at treeline elevations.Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 2.5

Valid until: Mar 14th, 2018 2:00PM